1. Field of the Invention
The present invention relates to a coffee filter material and a coffee filter bag. More particularly, the present invention relates to a coffee filter material usable for a coffee filter bag or drip type coffee filter vessel for obtaining a high-quality coffee extract, and to a coffee filter bag formed by using this material.
2. Description of the Related Arts
Various coffee extraction methods, such as a siphon method using an extracting tool, an espresso method, a meliol method, and a drip method are known, and the drip method is currently most widely used.
The flannel drip extraction method is most generally adopted, wherein a 40-count flannel formed by raising a thick woven cotton fabric is used for a filter bag for separating a coffee extract from coffee powder during a filtration extraction of coffee. This filter cloth, however, is thick, and if used over a long period, clogging occurs and coffee fat is adhered to the filter cloth, with the result that the filter cloth is contaminated, discolored, and impregnated with a smell. Accordingly, after the filter cloth is used, it must be washed with water, and should be immersed in water before using it again, and thus, for reasons of sanitation, great care is necessary. Accordingly, the flannel drip type extraction method is limited with regard to business use or for use by specific persons.
Furthermore, the paper drip type extraction method is defective in that, since a thick filter paper is generally used, a long time is required for the filtration and extraction. Although the paper drip extraction method is used for a small number of persons, if the amount of coffee powder is small, the filtration area is small, and thus hot water must be frequently and uniformly poured thereover, for an extraction of all of the coffee, and the required quantities of hot water must be measured in advance. Namely, many preliminary operations must be conducted before the extraction operation, and the extraction loss and extraction unevenness are conspicuous, and further, the temperature of the hot water is lowered during the extraction operation and thus it is necessary to reheat the water.
As pointed out above, a paper filter sheet or a nonwoven fabric filter sheet is generally used as the filter material for the extraction of coffee, and some of these conventional filter sheet materials for the extraction of coffee are not satisfactory because the effect of filtering and removing coffee particles (solids) is excessively high, the concentration or flavor of the obtained coffee extract is insufficient, and a long time is required for the extraction. Other conventional sheet materials are disadvantageous in that, since the effect of filtering and removing coffee particles is excessively low, the obtained coffee extract contains large-quantities of solid coffee particles, and the flavor or taste is degraded and precipitates are formed.
If a fine powder of coffee is extracted with hot water, an oil and fat component in the fine powder of coffee is additionally extracted, and thus a filter sheet material for extraction of coffee is required to appropriately remove this oil and fat component by adsorption.
Before the present invention, however, the filtering characteristics that should be possessed by a coffee filter sheet material for obtaining a high-quality coffee extract from a fine powder of coffee were little known.
For example, Japanese Unexamined Utility Model Publication Nos. 55-129667, 55-129668 and 55-129669 disclose a coffee bag formed of a filter sheet in which the distribution density of filtering fine pores having a pore size of 80 .mu.m or more is limited to 6 pores or less per cm.sup.2. In this coffee bag, however, only a conventional nonwoven fabric capable of substantially inhibiting a permeation of relatively large particles having a particle size of 80 .mu.m or more is used, and this coffee bag is still unsatisfactory as a filter material for fine particles of coffee. Moreover, with this coffee bag, to prevent a leakage of fine coffee particles, a preliminary treatment of separating and removing fine particles is necessary, and therefore, a utilization of components extracted from fine coffee particles is impossible. Still further, the extraction operation is complicated. Accordingly, this coffee bag is not completely satisfactory for obtaining a high-quality coffee extract.